Fuel cell stack systems are used as power sources for electric vehicles, stationary power supplies, and other applications. One known fuel cell stack system is the proton exchange membrane (PEM) fuel cell stack system that includes a membrane electrode assembly (MEA) comprising a thin, solid polymer electrolyte membrane having an anode on one face and a cathode on the opposite face. The MEA is sandwiched between a pair of electrically conductive contact elements which serve as current collectors for the anode and cathode, which may contain appropriate channels and openings therein for distributing the fuel cell stack system's gaseous reactants (i.e., H2 and O2 or air) over the surfaces of the respective anode and cathode.
PEM fuel cells comprise a plurality of the MEAs stacked together in electrical series while being separated by an impermeable, electrically conductive contact element known as a bipolar plate or current collector. The fuel cell stack systems are operated in a manner that maintains the MEAs in a humidified state. The level of humidity of the MEAs affects the performance of the fuel cell stack system. Additionally, if an MEA is operated too dry, the performance and useful life of the MEA can be reduced. To avoid drying out the MEAs, the typical fuel cell stack systems are operated with the MEA at a desired humidity level, wherein liquid water is formed in the fuel cell during the production of electricity. Additionally, the cathode and anode reactant gases being supplied to the fuel cell stack system are also humidified to prevent the drying of the MEAs in the locations proximate the inlets for the reactant gases. Traditionally, a water vapor transfer (WVT) unit is utilized to humidify the cathode reactant gas prior to entering into the fuel cell. See, for example, U.S. Pat. No. 7,138,197 by Forte et al., incorporated herein by referenced in its entirety, a method of operating a fuel cell stack system.
The basic components of a PEM-type fuel cell are two electrodes separated by a polymer membrane electrolyte. Each electrode is positioned on opposite sides of the membrane as a thin catalyst layer. Similarly, on each side of the assembly adjacent to each thin catalyst layer, a microporous layer (MPL) is coated on a gas diffusion substrate to produce a gas diffusion layer wherein the gas diffusion layer is the outermost layer on each side of the membrane electrode assembly (MEA). The gas diffusion substrate is commonly composed of non-woven carbon fiber paper or woven carbon cloth. The GDL is primarily provided to enable conductivity, and to allow gases to come in contact with the catalyst. The GDL works as a support for the catalyst layer, provides good mechanical strength and easy gas access to the catalyst and provides the electrical conductivity. The purpose of the microporous layer is to minimize the contact resistance between the GDL and catalyst layer; limit the loss of catalyst to the GDL interior and help to improve water management as it provides effective water transport. Accordingly, the electrodes (catalyst layers), membrane, microporous layers, and gas diffusion layer together form the membrane electrode assembly (MEA). The MEA is generally disposed between two bipolar plates to form a fuel cell arrangement.
As is known, hydrogen is supplied to the fuel cells in a fuel cell stack to cause the necessary chemical reaction to power the vehicle using electricity. One of the byproducts of this chemical reaction in a traditional fuel cell is water in the form of vapor and/or liquid. It is also desirable to provide humid air as an input to the fuel cell stack to maximize the performance output for a given fuel cell stack size. Humid air also prevents premature mechanical and chemical degradation of the fuel cell membrane.
The input air is typically supplied by a compressor while a water transfer device external to the stack is traditionally implemented in a fuel cell system to add moisture to the input air supplied by a compressor, the source of the moisture often coming from the product-water-laden stack cathode outlet stream. These components among many other components in a traditional fuel cell system contribute to the cost of the fuel cell system and also require packaging space. In many applications, such as but not limited to a vehicle, packaging space is limited.
Accordingly, there is a need to integrate components of a fuel cell system where possible at a reasonable cost.